DE69304756T2 - Motor servo system - Google Patents

Description

BACKGROUND OF THE INVENTION Field of invention

Generally, the invention relates to a motor servo system. More particularly, the invention relates to a motor servo system used in a servo system for suppressing irregularities of an FG signal caused by a drum motor of a VTR (Video Tape Recorder) leading to irregularities in rotation, or a servo system for controlling a motor, such as a shaft motor of a VTR, in which desired response characteristics cannot be achieved due to offset, load change, etc.

Description of the state of the art

As a conventional motor servo system 1 in which the irregularities of an FG signal (hereinafter referred to simply as FG irregularity) can be suppressed to remove a signal component of these FG irregularities from a motor control signal, there is a circuit in which an analog notch filter 2 is inserted as shown in Fig. 7 or a circuit in which a digital notch filter 3 is inserted as shown in Fig. 8. Furthermore, as the circuit shown in Fig. 8, Digital notch filter 3, for example, a circuit as shown in Fig. 9 can be used.

In addition, as a known motor servo system 1 for controlling a shaft motor 4 of a VTR, there is a circuit as shown in Fig. 10 in which speed detection and phase detection are performed based on the FG signal, and these detection signals are synthesized with each other, and then a motor control signal is applied to the shaft motor 4 via a low-pass filter section 5, a D/A converter section 6, etc.

In the analog notch filter 2 used in the motor servo system 1 shown in Fig. 7, there is a case that a deviation in the center frequency of a notch occurs due to the fluctuation of electronic parts and therefore the effect of the notch decreases.

In the digital notch filter used in the motor servo system 1 shown in Fig. 8, no deviation of the center frequency occurs, but the RAM (Random Access Memory) time and the CPU (Central Processor Unit) time become very long. In particular, when the digital notch filter is used to remove FG irregularities of the drum, the longer the sampling times for one rotation become, the larger the number of delay times becomes, and therefore the CPU time becomes long. On the other hand, in such a system in which a servo control microcomputer and a system control microcomputer are included in the same microcomputer, it becomes impossible to sufficiently increase the sampling frequency by the servo microcomputer, i.e., the number of delay times of the notch, because the CPU time cannot be devoted only to the servo control microcomputer, and therefore sufficient security cannot be obtained.

In addition, in the case where a motor having a large displacement or load change is controlled by the motor servo system 1' shown in Fig. 10, since it was necessary to make the servo gain very large, there was no other way in the past than to increase the servo gain by increasing the sampling frequency. However, when a motor is miniaturized, there is a problem that the displacement or load change becomes large and, on the other hand, the sampling frequency decreases because the magnetization number of the motor is reduced, and therefore it becomes impossible to sufficiently suppress the irregularities of the motor rotation.

SUMMARY OF THE INVENTION

It is therefore an essential object of the invention to provide a motor servo system in which a motor can be stably controlled with a simple software even when FG irregularities occur.

Another object of the invention is to provide a motor servo system in which it is possible to increase the servo gain even when a disturbance such as a load change occurs.

A motor servo system according to the invention controls a motor based on a speed detection signal and a phase detection signal. The motor servo system comprises: first synthesizing means for synthesizing the speed detection signal and the phase detection signal with each other at a predetermined synthesizing ratio to produce a synthesized signal; equivalent motor means having a transfer function representative of a transfer characteristic of the motor and for producing a detection signal based on the synthesized signal; first comparison means for comparing the synthesized signal and the detection signal; and motor control signal generating means for generating a motor control signal by which the motor is to be controlled, based on the synthesized signal and an output signal of the first comparison means.

According to the invention, the speed detection signal is generated by a speed detection section which generates a speed detection signal based on, for example, an FG signal from the motor. A phase detection section generates a phase detection signal based on, for example, an FG signal from the motor, or by integrating the speed detection signal. The first synthesizing means receives the speed detection signal and the phase detection signal and generates the synthesized signal, which is applied to the motor control signal generating means and the first comparing means, respectively.

The equivalent motor means is a kind of software motor and has a transfer function equal to or similar to that of the motor to be controlled. The equivalent motor means receives the output signal of the first synthesizing means through, for example, a low-pass filter means. The detection signal of the equivalent motor means is compared with the synthesizing signal of the first synthesizing means, and therefore the output of the first comparing means becomes a signal representing only an FG irregularity component or a noise component. Therefore, the motor control signal output from the motor control signal generating means does not contain such an FG irregularity component or noise component.

According to the invention, the motor can be stably servo-controlled.

The above and other objects, features, aspects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a functional block diagram showing an embodiment of the present invention;

Fig. 2 is a functional circuit diagram showing an equivalent motor portion of the embodiment of Fig. 1 ;

Fig. 3 is a functional circuit diagram showing a low-pass filter section having a transfer function corresponding to that of the equivalent motor section;

Fig. 4 is a graph showing a gain characteristic of the functional circuit of Fig. 2;

Fig. 5 is a functional block diagram showing another embodiment of the present invention;

Fig. 6 is a graph showing beat and noise of the embodiment of Fig. 5;

Fig. 7 is a functional block diagram showing the prior art;

Fig. 8 is a functional block diagram showing another prior art;

Fig. 9 is a functional circuit diagram showing a digital notch filter used in the prior art of Fig. 8; and

Fig. 10 is a functional circuit diagram showing still another prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Fig. 1, a motor servo system 10 of the shown embodiment is used for removing the FG irregularity in a drum servo system by using stable control, and includes a servo control microcomputer 12. As the microcomputer 12, a servo microcomputer "CXP80724" is used.

The microcomputer 12 includes a speed detecting section 14 and a phase detecting section 16. A PG pulse and an FG pulse from a drum motor 18 are amplified by a PG amplifier 20 and an FG amplifier 22, and then the PG pulse and the FG pulse are applied to the speed detecting section 14 and the phase detecting section 16, respectively.

In the speed detecting section 14, a speed detecting signal is obtained by counting the period of the FG pulse. In the phase detecting section 16, a phase detecting signal is obtained by comparing the phase of the PG pulse and the phase of a vertical synchronization signal Vsync applied in a recording mode by connecting from a terminal 24a through a switch 24. In the reproducing mode, the switch 24 is connected to a terminal 24b, and therefore a reference signal is applied to the phase detecting section 16, and accordingly a phase detecting signal is obtained by detecting the phase difference between the reference signal and the PG pulse.

The speed detection signal and the phase detection signal are combined or synthesized by a synthesizing section 26, thereby obtaining a detection signal. The detection signal is via a low-pass filter section 28 to a motor control signal. The motor control signal is applied to both a comparator section 10 and an equivalent motor section (software motor) 34 of an observer device 32.

The equivalent motor section 34 has a transfer characteristic equivalent to that of the drum motor 18. For the equivalent motor section 34, a circuit shown in Fig. 2 is used. In addition, the equivalent motor section having the same transfer function may be represented by an RC low-pass filter shown in Fig. 3. The transfer function of the circuit shown in Fig. 2 is represented by the following equation.

y(nT) = K₁x(nT) + K₂x(nT-T) + K₃y(nT-T)

= y(nT-T) + a{x(nT) - y(nT-T)} + b{x(nT) - x(nT-T)}

... (1)

where x is an input signal, y is an output signal and T is the sampling frequency.

A gain characteristic of the transfer function represented by Equation 1 is shown in Fig. 4. In Fig. 4, the frequencies f₁ and f₂ are represented by the following Equations 2 and 3, respectively.

f1; = a/π (2b + a)T ... (2)

f2; = a/π (2 a - a)T ... (3)

When 2b+a=0, then f1=∞ (infinity) and accordingly, the circuit shown in Fig. 2 operates as a low-pass filter. Accordingly, the circuit shown in Fig. 2 becomes a circuit equivalent to the drum motor 18.

By comparing the detection signal from the equivalent motor section 34 and the detection signal from the synthesizing section 26 by means of a comparator section 36, a comparison signal A is obtained. In the comparator section 30, the comparison signal A is subtracted from the motor control signal output from the low-pass filter section 28. At this time, no FG abnormality occurs at the equivalent motor 34 although the FG abnormality exists at the drum motor, and accordingly, a signal spectrum of only the FG abnormality will be included in the comparison signal (A). Therefore, by subtracting the signal spectrum for the FG abnormality, i.e., the comparison signal (A), from the motor control signal, it is possible to remove only the FG abnormality component from the motor control signal.

The motor control signal from which the comparison signal (A) has been subtracted is D/A converted by a D/A converter section 38 of a PWM system, and then the motor control signal is smoothed by a resistor R and a capacitor C so as to be applied to the PWM driver 42, whereby the drum motor 18 can be controlled.

Since no DC gain reduction occurs in the motor servo system 10 unlike a digital notch filter, it is possible to remove the FG irregularity components included in both the speed detection signal and the phase detection signal. In addition, it is possible to also remove false signal spectrums other than the FG irregularity.

In Fig. 5, a motor servo system 10' according to another embodiment stably controls a shaft servo system (software servo) of an 8 m/m VTR. The motor servo system contains a servo control microcomputer 42. The servo microcomputer "CXP80724" can also be used as the microcomputer 42.

The microcomputer 42 includes a speed detecting section 44 to which an FG pulse from a shaft motor 46 is input after being amplified by an FG amplifier 48. By counting the period of the FG pulse, a speed detecting signal is obtained by the speed detecting section 44. A duty ratio of the speed detecting signal is corrected by a duty correcting section 50.

In addition, in a recording mode, phase detection is generated by integrating the speed detection signal by a phase detection section 52. In a playback mode, a reference signal to be integrated by the phase detection section 52 is changed in accordance with a track signal. In the shown embodiment, an integration type of phase detection is used in both the recording mode and the play mode. In addition, an analog signal from an ATF processing section 54 is A/D converted in an A/D converter section 56, and data from the D/A converter section 56 is filtered by a low-pass filter section 58 and a comb-type filter 60 and then applied to a synthesizer section 62. In the synthesizer section 62, the track signal is generated by adding a reference signal to the data.

Then, the speed detection signal from the power-on correction section 50 and the phase detection signal from the phase detection section 52 are supplied to a synthesizing section 64, and a synthesized signal is generated. The synthesizing ratio at this time is set such that, as an example of this embodiment, Speed detection signal : phase detection signal = 64:1. However, such a synthesizing ratio can be adjusted according to a characteristic of the servo system.

Then, an optimized motor control signal (b) is generated by passing the synthesizing signal (a) through a low-pass filter section 66. The motor control signal (b) is applied to a synthesizing section 68 and to a synthesizing section 72 of an observer device 70. A comparison signal (c) from the comparing section 76 (which will be described later) is fed back to the synthesizing section 72, and the motor control signal (b) and the comparison signal (c) are then synthesized together with a weighting of, for example, 4:1.

A synthesized signal of the motor control signal (b) and the comparison signal (c) is applied to the equivalent motor section (software motor) 74 having a transmission characteristic corresponding to the shaft motor 46.

In the comparator section 76, a detection signal (d) from the equivalent motor section 74 and the synthesizing signal (a) from the synthesizing section 64 are compared with each other at a weighting ratio of, for example, 1:1, to obtain the comparison signal (c). The comparison signal (c) is fed back to the synthesizing section 72 as described above and applied to the synthesizing section 68.

In the synthesizing section 68, the motor control signal (b) and the comparison signal (c) are combined or synthesized with a weighting ratio of, for example, 4:1. Needless to say, such synthesizing ratios are used in the synthesizing sections 66 and 72. can also be adjusted according to the characteristics of the servo system.

A synthesizing signal from the synthesizing section 68, i.e., the motor control signal, is D/A converted by a D/A converting section 78 of a PWM system and then smoothed by a resistor R and a capacitor C so as to be applied to a PWM driver 80, whereby the shaft motor 46 can be controlled.

For such a motor servo system 10', a spectrum given by a relative value of a beat and the noise of the shaft motor is shown in Fig. 6. As can be clearly seen from Fig. 6, the spectrum A of the motor servo system 10' is greatly reduced in comparison with a spectrum B in the prior art within a servo frequency range of about 100 Hz. Thus, in the motor servo system 10', a spectrum component due to a difference between the ideal motor and the actual motor can be fed back to a large extent, and therefore, the effect of suppressing load change becomes large in comparison with a servo system of the prior art.

Needless to say, although individual functions to be executed by the servo control microcomputer have been illustrated as respective function blocks in the embodiment of Fig. 1 and the embodiment of Fig. 5, in practice, the respective function blocks may be executed by execution programs. However, such respective function blocks may of course be implemented by means of hardware.

Claims (7)

1. Motor servo system (10, 10') for controlling a motor (18, 46) based on a speed detection signal and a phase detection signal, comprising first synthesis means (26, 64) for synthesizing the speed detection signal and the phase detection signal with each other at a predetermined synthesis ratio to generate a synthesized signal, characterized in that the system further comprises: equivalent motor means (34, 72, 74) with a transfer function representative of a transfer characteristic of the motor for generating a detection signal based on the synthesized signal, first comparison means (36, 76) for comparing the synthesized signal and the detection signal, and motor control signal generating means (30, 68) for Generating a motor control signal by which the motor is to be controlled on the basis of the synthesized signal and an output signal of the comparison means. 2. Motor servo system according to claim 1, wherein the motor control signal generating means comprises second comparison means (30) for comparing the output signal of the first comparison means (36) and the synthesized signal with each other. 3. Motor servo system according to claim 1 or 2, wherein the motor control signal generating means comprises second synthesis means (68) for synthesizing the output signal of the first comparison means (76) and the synthesized signals with each other with a given synthesis ratio. 4. A motor servo system according to any one of claims 1 to 3, wherein the equivalent motor means comprises an equivalent motor (74) and third synthesis means (72) for synthesizing the synthesized signal and the output signal of the first comparison means (76) with each other at a predetermined synthesis ratio, the output signal of the third synthesis means (72) being supplied to the equivalent motor (74), an output signal of the equivalent motor being supplied to the first comparison means as the detection signal. 5. A motor servo system according to claim 1, further comprising low pass filter means (28, 66) for filtering the synthesized signal, the equivalent motor means (34, 72, 74) receiving the output of the low pass filter means to generate the detection signal. 6. Motor servo system according to claim 5, wherein the motor control signal generating means comprises second comparison means (30) for comparing the output signal of the first comparison means (36) with the output signal of the low-pass filter means (28) with each other at a predetermined synthesis ratio. 7. Motor servo system according to claim 5 or 6, wherein the equivalent motor means comprises an equivalent motor (74) and third synthesis means (72) for synthesizing the output signal of the low-pass filter means (66) and the output signal of the first comparison means (76) with each other at a predetermined synthesis ratio, the output signal of the third synthesis means (72) being supplied to the equivalent motor and the output signal of the Equivalence motor (74) is supplied to the first comparison means (76) as the detection signal.